FIG. 1 illustrates side and plan views of a rotary bond head 100 during pattern recognition (“PR”) alignment. The rotary bond head 100 has a wedge bonding tool 114 at its bottom end and in attached to a main bracket 116 for mounting the bond head 100.
In such existing bond head designs, a bonding wedge center 102 (also a rotary center of a theta axis of the bond head 100) is not aligned with a PR optical center 104 of the bond head 100. A PR optics assembly 108 which provides coaxial light and is operative to inspect a substrate such as a lead frame 112 to be bonded is located and mounted next to the bonding wedge center 102. It is coupled with the theta axis of the bond head 100. In this configuration, there is a distance separating the bonding wedge center 102 and the PR optical center 104. This distance, measured from a rotary center line 103 to an optical center line 105, is called the bond tip offset or BTO 106. A PR alignment camera assembly 110 is mounted on an XY positioning table vertically above the PR optics assembly 108.
An image of a target surface can only be captured when the bond head 100 is fixed at a particular theta orientation where the PR optics assembly 108 and the PR alignment camera assembly 110 are located over the target surface for conducting PR alignment on the target surface. Therefore, during a bonding sequence, the bond head 100 needs to rotate to a predetermined angle for PR alignment first, and thereafter, it needs to move and rotate such that the bonding wedge center 102 and bond head rotary angle is aligned with a target bonding direction of the wire.
FIGS. 2A to 2C illustrate a conventional bonding sequence including PR alignment. In FIG. 2A, the bond head 100 is positioned at a particular theta orientation for PR alignment of the target object. After the locations of bonding points and an orientation of a wire connection is determined, the bond head 100 will be moved sideways and rotated such that the bond wedge center 102 is aligned with the target bonding direction as shown in FIG. 2B and FIG. 2C. Both the XY motion and theta rotation are necessary for BTO movement and wedge rotation. The latter rotates the bonding tool 114 to the required bonding orientation.
Since movement of the bond head 100 in the XY and theta directions are necessary for PR alignment prior to bonding each wire connection, the overall bonding time will be slower due to this additional motion that has to be conducted apart from the actual bonding operation.